Tools for cutting holes in various materials such as sheet metal generally fall into two types, those which operate by cutting or removing the entire interior area of a circle and those which operate by cutting only the circumferential area of a circle thereby producing an interior circular plug during the cutting operation. A conventional fluted drill is an example of the former type of tool. Such tools have the disadvantage of requiring substantially more cutting activity in order to produce the desired hole since the entire volume of the materia must be cut away to form the desired hole. Over a certain diameter, it is much more efficient and generally quicker to utilize a tool which cuts a circumferential circle for removing the metal as a plug. Such tools are generally known as trepanning tools. Tools of this type require substantially less cutting to achieve a desired hole and therefore provide large diameter holes quickly and with substantially less energy consumption.
The use of trepanning tools which cut only the circumferential area of circles to provide large diameter holes is known. Such tools generally comprise an elongated tubular cutting head having cutting blades or tips secured thereto which engage a work piece to shave or cut portions thereof to define the circumference of a circle upon rotation of the tool. Accordingly, as cutting of a work piece is effected, a center plug is produced which is received in the center area of the elongated tubular cutting head. Tools of this type have been available for cutting holes having diameters ranging from approximately less than an inch to holes having extremely large diameters for example up to 10 inches or more. Such large diameter trepanning tools are generally associated with lathe type machines which are fixedly mounted for producing holes in an automated fashion. Generally, such trepanning tools are therefore rigidly aligned with the material to be cut which is usually also clamped or fixed to prevent movement. While such applications are known in the art, there has been a continuing effort to produce tools suitable for use in a hand held fashion which will provide a relatively precise and smooth hole in thin sheet metal for use, for example, in field construction such as by an electrician in cutting holes in electrical boxes. In addition, it is desirable to cut holes in other types of sheet metal such as stainless steel, which is finding more use in home and building construction.
Various examples of hole cutting devices that are adapted for use with a hand held rotational drive mechanism, such as a hand held drill, exist. One type of hole saw is essentially a cylindrical tube having a leading edge with serrations or cutting teeth. Typically, a pilot drill bit that extends from the cylindrical tube is incorporated to act as a guide for aligning the hole saw. One problem with this type of hole saw is that the width of the teeth are more or less limited to the width of the cylindrical body of the hole saw, which is generally relatively thin. As a result, the serrations or cutting teeth are prone to breakage, which requires replacement.
Another example of a hole saw is found in U.S. Pat. No. 5,049,010, which discloses a hole saw that utilizes a single carbide tip permanently secured with a rotatable body. While such a hole saw has performed adequately, a serious drawback with such design is due to the fact that the only cutting edge, namely the carbide tip, is permanently secured or bonded to the body of the hole saw. When the carbide tip is worn, dulled, or broken, the entire hole saw must be replaced.
The present invention overcomes the shortcomings of the prior art and provides an effective device for cutting holes in metal.